Moisture responsive device

ABSTRACT

A device responsive to the presence of moisture in soil for controlling the flow of irrigating water to the soil being monitored. The device comprises a cylindrical body of capillary material of controlled porosity having one end surface exposed to the moisture in the soil through a wick. The body is provided with capillary passageways connecting the ends of the body. Moisture is drawn from the wick along these passageways by capillary action displacing air which moves toward the other end of the body. A casing sealed to the body and containing a diaphragm provides an enclosed volume into which displaced air is compressed. The displaced air generates a pressure within the enclosed volume which moves the diaphragm to operate a valve shutting off the irrigating water.

United States Patent Treirat July 24, 1973 MOISTURE RESPONSIVE DEVICE[76] Inventor: Eduard Trelrat, 576 Broughton Pmfmry Exam":'er ChafleSMyhre Ave. Bloomfield Ni 07003 Assistant Exammer--R. H. Lazarus lAtt0rney-Gerald Durstewitz [22] Fi ed: Aug. 17, 1971 21 Appl. No.:172,408 [571 ABSTRACT A device responsive to the presence of moisture insoil for controlling the flow of irrigating water to the soil [52] US.Cl. 73/73, 61/13, being monitored. The device comprises a cylindricalbody of capillary material of controlled porosity having one end sprfaceexposed to the moisture in the soil I 1 0 7 1/12 through a wick. Thebody is provided with capillary l l l 73/73 7/38'1 passagewaysconnecting the ends of the body. Moisture is drawn from the wick alongthese passageways by cap- [56] References Cited illary action displacingair which moves toward the UNITED STATES PATENTS other end of the body.A casing sealed to the body and 3,091,115 5/1963 Roberts...., 73/73containing a diaphragm provides an enclosed volume 2,445,717 7/1948Richards 61/13 X into which displaced air is compressed. The displaced3,642,204 2/ 1972 MFCIOSkeY 239/63 air generates a pressure within theenclosed volume 2,672,490 14/1954 f g 61/13 which moves the diaphragm tooperate a valve shutting i'ffil'fiifi 21:22: sass-"- 23?: 3,244,3724/1966 I 137/78 10 Claims, 2 Drawing Figures Hanner PAIENIEU 3. 747. 399

sum 1 or 2 FIG.

PATENTEU 3. 747. 399

SHEET 2 UP 2 FIG. 2

MOISTURE RESPONSIVE DEVICE BACKGROUND OF THE INVENTION The presentinvention relates to moisture sensitive devices, and, more particularly,to such devices which generate a gaseous pressure in response to thepresence of moisture.

It is well known in the field of agriculture, that satisfactory plantgrowth is achieved when the soil is subjected to a wetting and dryingcycle which permits proper aeration of the soil. To achieve a maximumrate of plant growth, the degree to which the soil is wetted and thedegree to which it dries out should be closely controlled. If the soilis of the type which readily holds water, and an overabundance of wateris added to the soil during the wetting portion of the cycle, the plantroots are subject to an overly wet condition for too long a time andthere is a danger of the roots rotting. On the other hand, if the soildries out too much between wettings, the plants will wilt. Bothover-watering and overdrying of the soil can both interfere with thegrowth of the plant and cause damage to the plant so that furture growthis adversely effected.

It has been proposed in U.S. Pat. No. 2,445,717 to regulate the wateringof plants by utilizing a porous ceramic body buried in the soil at thebottom of a sealed vertical tube filled with water. A vacuum sensitivediaphragm is provided in the tube and operates a valve which controlsthe irrigation system. When the soil surrounding the ceramic body driesout, the water in the tube seeps through the pores of the ceramic bodyinto the soil. As water flows from the tube, the air pressure in thesealed tube drops below atmospheric and draws in the diaphragm turningon a water valve. The irrigating water is absorbed by the soil and whenthe soil surrounding the ceramic body is saturated the flow of waterthrough the ceramic reverses and the pressure in the tubeapproaches'atmospheric. The diaphragm then moves outwardly and the watervalve closes terminating the watering.

In the prior art system, as disclosed in lines 11 through 28 of column 5ofthe patent, the water in the tube is gradually replaced by air and itis necessary to periodically replenish the water in the tube. For thisreason, it is necessary that the tube extend about the surface of theground and be provided with a cap for adding the water. The extension ofthe tube above the ground interferes with the cultivation of the soiland requires that the tube beof sufficient length to extend from theroots of the plants to the surface of the ground.

SUMMARY OF THE INVENTION 7 It is an object of the present invention toprovide a novel moisture responsive device.

Another object is to provide such a device which generates a gaspressure when exposed to moisture.

Another object is to provide such a device which does not requireperiodic servicing.

Another object is to provide such a device for controlling the wateringof plants and which can be completely buried.

Another object is to provide such a device in which the gaseous pressuregenerated produces mechanical motion.

Another object is to provide such a device which operates a valvecontrolling the watering of the soil.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of theinvention has been chosen for the purposes of illustration anddescription, and is shown in the accompanying drawings, forming a partof the specification, wherein:

FIG. 1 is an elevational view, in section, showing a moisture responsivedevice according to the present invention positioned in soil andconnected to a water supply for irrigating the soil.

FIG. 2 is a longitudinal sectional view of a moisture responsive deviceaccording to the present invention which is connected to a capillarysize tube for connection to a pressure sensitive device.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of thedrawings, there is shown a moisture responsive device 10 buried in soil,a sheet 11 of wicking material also buried in the soil against which themoisture sensing surface of the device 10 is held in contact a valve 12mounted on the device 10 to be controlled thereby, a tube 13 connectingthe inlet of the valve 12 to a source of water (not shown), and a tube14 connecting the outlet of the valve 12 to the sheet 11 of wickingmaterial.

The device 10 includes a tubular casing 15 in which is positioned a massof capillary material 16 having a controlled porosity. An annularsealing member 17 is positioned between the casing 15 and the material16. The lower end of the casing 15 is provided with an annular flange 19and the wick material 11 is clamped between the flange and a plate 20 bybolts 21 so as to be in contact with the lower surface of the mass ofmaterial 16. The upper end of the casing 15 is provided with an internalannular recess 22 in which is positioned an annular compressible plasticgasket .23 and a porous disc 24 having a concave upper surface. A springmetal oil canning diaphragm 25, overlies the disc 24. An annular plasticgasket 26 surrounds and extends over the outer edge of the disphragm 25.A circular cap 27 is threaded onto the upper end of the casing 15 and isprovided with a shoulder 29 which engages and squeezes the gasket 26providing a pressure seal to prevent air flow around the edge of thediaphragm. The cap 27 defines, with the diaphragm 25, a chamber 30 andthe cap is provided with a vent hole 31 in its side.

wall 32 and a bore 34 in its top wall 35. A pin 36 extends from thechamber 30 through the bore 34 and is formed with a head 37 at its lowerend in contact with the diaphragm 25. An 0 ring seal 38 is positioned inthe top wall 35 at the bore 34 to provide a liquid seal between the wall35 and the pin 36.

The mass of material 16 is composed of spherical glass beads havingdiameters ranging from 0.0029 to 0.0017 inches. In assembling thedevice, the body and the plate are clamped to the wick material, thegasket 23 and the sealing member 17 are put in place, and the beads arepoured into the body. The body is tapped or shaken to settle the beads,the disc 24 and the diaphragm 25 are put in place, and the cap 27(carrying the gasket 26 and the pin 36) is screwed down onto the body toforce the beads into close contact. The air spaces between the beads areextremely small (being of the order of 0.001 inch radius) and provide aplurality of interconnected capillary passageways extending between thesurface of the mass 16 in contact with the wick material and the surfacein contact with the porous disc 24. The annular sealing member 17 may bea sleeve of rubber or other-soft plastic material or a coating of epoxyresin or the like. The beads around the outer periphery of the mass 16are partially embedded in the sealing member 17 to minimize the size ofthe open spaces in this area. This may be accomplished, in the case of adeformable sleeve, by placing a compressive force on the beads bythreading down the cap 27, or, in the case of a material like epoxyresin, the beads are introduced into the body 15 while the material isstill in a semi-fluid state.

The valve 12 includes a cup shaped cap 40 threaded onto the top of thecap 27 to provide a chamber 41. The cap 40 is formed with an inletpassageway 42 receiving the tube 13 and an outlet passageway43 receivingthe tube 14. An 0 ring 44in the passageway 42 provides a valve sealwhich is engaged by the stem 36 to control the flow of water from thetube 13 to'the tube 14. In operation, the valve 12 is normally open andwater flows from the tube 13 into the chamber 41 and through the tube 14to the wick'material 11. The

. water in the wick material is drawn, by capillary action,

into the passageways formed by the spaces between the beads of the massof material 16. The movement of the water along these passagewaysdisplaces the air in the passageways. The displaced air cannot flow pastthe diaphragm 25, and, as the water progressively moves toward thediaphragm, the air is forced into a progressively smaller volume and iscompressed. When the air pressure reaches a predetermined valve the oilcanning diaphragm operates and snaps up to the position shown in thedotted lines. The stem 36 is then thrust into the passageway 42 andengages the O ring 44 to shut off the water flow to the wick 11. v

The diaphragm 25 maintains this positionuntil the soil and the wick lldries and draws sufficient water from the capillary passageways in thematerial 16 to relieve the air pressure on the diaphragm. The diaphragmthen snaps down to its original, position allowing water to once againflow to the wick 11.

The soil is thereby passed through repeated cycles of wetting and dryingto provide conditions for maximum plant growth.

The operation of this device is dependent upon the capillary material 16having a closely controlled porosity. The air pressure which can begenerated by water being drawn by capillary action along a capillarytube is inversely proportional to the radius of the tube. The pressurewith which water is drawn up a capillary tube is given by the formula P2 St/r where P is pressure in pounds per square inch (PS1), St is thesurface tension of the liquid in pounds per inch, and r is the radius ofthe capillary tube in inches.

The motion of the water up a closed end capillary tube stops when theair pressure acting on the upper surface of the water column equals thepressure given by the formula. Thus, if a capillary tube having aconstant radius of 0.0005 inch is sealed at the top end, water will risein the tube until the air therein has been compressed to 1.65 PS1, avalue equal to that given by the formula under these conditions.

If, however, the capillary tube is not of uniform crosssection, thepressure developed tends to be controlled by the radius of the widestportion of the tube. In a closed end tube having a 0.0005 inch radiusthroughout the majority of its length and having portions which widenout to 0.005 inch, the movement of the water would be halted at thefirst wide portion if the air pressure in the tube then equaled orexceeded 0.165 PS1. If at that time the air pressure was less than thisvalue, the water would be drawn past this wide point. If the next widepoint was spaced at a sufficient distance along the tube, the pressurein the tube could reach 1.65 PS1. However, if the wide portions wereclosely spaced the final pressure developed would be about the 0.165 PS1value. Should the air pressure reach a value considerably above 0.165PS1 as the water is drawn from one wide section to a second, the waterwill stop short of the widest part of the second section at a point ofintermediate radius, where the air pressure is balanced by the pressureacting on the water.

Where, as in this invention, there are a plurality of capillary tubeswhich lead into a common chamber (rather than being individually sealedoff) the pressure generated in the chamber will be limited by the effect1 of the capillary tubes generating the least pressure. It is extremelyimportant, therefore, that the mass of capillary material have a closelycontrolled porosity.

Referring now to FIG. 2, there is shwon a moisture responsive device 50according to the present invention modified for connection to recording,indicating, or measuring apparatus. The device 50 includes a tubularcasing 51 having a flange 52, and a sheet 54 of wick material is clampedbetween the flange 52 and a plate 55. The casing 51 is filled with amass 56 of of capillary material having a controlled porosity. Anannular band of of epoxy resin 57 provides a seal between the mass 56and the inner surface of the casing 51. A porous 59 is positioned on topof the mass 56. A stepped plug 60 carrying an O ring seal 61 is heldagainst the disc 59 by means of an annular nut 62 threaded onto the body51. The plug 60 is provided with a central bore in which a capillarytube 64 is sealed. The tube 64 may be connected to apparatus suitablefor indicating, measuring or recording the pressure or volume of the airdisplaced when the sheet 54 is wet by a liquid and the liquid movesalong the capillary passageways in the material 56.

A specific embodiment constructed according to FIG. 2 was employed tomeasure the volume and pressure of the air displaced from a mass ofcontrolled porosity material in response to the wetting of the wickmaterial. In this specific embodiment the inside diameter of the body 51was 1 inch, the length of the body was 2.5 inches, the mass was composedof glass beads having a range of diameters from 0.0029 to 0.00l7 inches,the wick 54 was composed of polypropilene carpeting, and the wick wassaturated with water.

In testing the air displacement of the unit, the capillary tube 64 wasconnected to a manometer, the wick 54 was saturated, and the volume ofair displaced through the tube 64 was continuously measured. It wasfound that 5 minutes after saturation of the wick, 0.010 cubic inches ofair had been displaced, and after minutes 0.032 cubic inches of air hadbeen displaced.

In another test, the capillary tube was connected to a pressuremeasuring instrument. The volume of the capillary tube and the interiorof the measuring instrument was approximately 0.005 cubic inches. Thewick was saturated and the following pressure readings were achieved atthe stated intervals from the time of saturation of the wick: 5 minutes0.200 pounds per square inch; 30 minutes 0.392 pounds per square inch; 1hr. 36 minutes 0.443 pounds per square inch. While these airdisplacement and pressure valves are small, they are sufficient tooperate an actuating device such as a diaphragm for controlling a valve.If desired, higher pressures can be achieved-by reducing the crosssectional dimensions of the capillary passageways (for example by usingsmaller glass beads) and greater air displacement can be achieved byusing a mass 56 of greater volume.

While the subject invention has been described herein in connection withplant irrigation, it is to be understood it can be used for otherpurposes to control liquid flow to an absorbing medium or to monitor theliquid content of such a medium.

It will be seen from the foregoing that the present invention provides anovel moisture responsive device which generates a gaseous pressure whenexposed to moisture, can be completely buried in a liquidabsorbing'medium to control the flow of liquid to that medium, and doesnot require periodic servicing.

I claim:

1. A device for generating a positive gaseous pressure in response tothe presence of moisture in a medium comprising a body of controlledporosity capillary material having a first surface portion to be placedin contact with the medium and a second surface portion spaced from saidfirst surface portion, said body having uniformly minute capillarypassageways filled with gaseous medium of atmospheric pressure when themedium is dry, said capillary passageways effectively connecting onlysaid first and second surface portions whereby moisture in the medium isdrawn by capillary action along said passageways and displaces thegeneous medium therein toward said second surface, and means sealed tosaid body providing an enclosed volume in communication with said secondsurface for confining the displaced gaseous medium to an extent suchthat a pressure is produced in said volume which is detectably aboveatmospheric when moisture is present in the medium.

2. A device according to claim 1 wherein said body containsmulti-directional capillary passageways and includes a sealed thirdsurface portion defining a peripherial band between said first andsecone surface portions to provide effective connection only betweensaid first and second surface portions.

3. A device according to claim 1 wherein the maximum effective radius ofeach of said passageways is about 0.0.01 inches.

4. A device according to claim 2 wherein said means providing saidenclosed volume is in sealing relationship with said third surfaceportion.

5. A device according to claim 2 including pressure responsive means insaid volume for converting changes in pressure into mechanical motion.

6. A device according to claim 5 including a porous member between saidsecond surface and said pressure responsive means.

7. A device according to claim 1 including a casing member surroundingsaid body between the first and second surface portions thereof, a capmember carried by said casing member providing the enclosed volume, anda pressure responsive member positioned in said volume between saidsecond surface and said cap member to be moved by gaseous mediumdisplaced from said body of controlled porosity material.

8. A device according to claim 7 wherein said body containsmulti-directional capillary passageways and means are included providinga peripherial seal between the inner surface of said casing member andthe outer surface of said body between said first and second surfaceportions thereof.

9. A device according to claim 1 including pressure responsive means insaid volume for converting changes in pressure into mechanical motion.

10. A device according to claim 1 wherein said enclosed volume has a gascapacity which is less than the total volume of said body.

1. A device for generating a positive gaseous pressure in response tothe presence of moisture in a medium comprising a body of controlledporosity capillary material having a first surface portion to be placedin contact with the medium and a second surface portion spaced from saidfirst surface portion, said body having uniformly minute capillarypassageways filled with gaseous medium of atmospheric pressure when themedium is dry, said capillary passageways effectively connecting onlysaid first and second surface portions whereby moisture in the medium isdrawn by capillary action along said passageways and displaces thegeneous medium therein toward said second surface, and means sealed tosaid body providing an enclosed volume in communication with said secondsurface for confining the displaced gaseous medium to an extent suchthat a pressure is produced in said volume which is detectably aboveatmospheric when moisture is present in the medium.
 2. A deviceaccording to claim 1 wherein said body contains multi-directionalcapillary passageways and includes a sealed third surface portiondefining a peripherial band between said first and secone surfaceportions to provide effective connection only between said first andsecond surface portions.
 3. A device according to claim 1 wherein themaximum effective radius of each of said passageways is about 0.001inches.
 4. A device according to claim 2 wherein said means providingsaid enclosed volume is in sealing relationship with said third surfaceportion.
 5. A device according to claim 2 including pressure responsivemeans in said volume for converting changes in pressure into mechanicalmotion.
 6. A device according to claim 5 including a porous memberbetween said second surface and said pressure responsive means.
 7. Adevice according to claim 1 including a casing member surrounding saidbody between the first and second surface portions thereof, a cap membercarried by said casing member providing the enclosed volume, and apressure responsive member positioned in said volume between said secondsurface and said cap member to be moved by gaseous medium displaced fromsaid body of controlled porosity material.
 8. A device according toclaim 7 wherein said body contains multi-directional capillarypassageways and means are included providing a peripherial seal betweenthe inner surface of said casing member and the outer surface of saidbody between said first and second surface portions thereof.
 9. A deviceaccording to claim 1 including pressure responsive means in said volumefor converting changes in pressure into mechanical motion.
 10. A deviceaccording to claim 1 wherein said enclosed volume has a gas capacitywhich is less than the total volume of said body.